The Glasgow team tested 479 shop-bought products from leading manufacturers, including Heinz, Cow & Gate and Boots, and found few were ideal for the job.

Most contained fewer nutrients than homemade food, and only as much as the breast milk they were supplementing.

And their sweet taste may steer the infant palate towards unhealthy choices, the researchers fear.

It's processed food that's been put in a jar so it's not that surprising that it does not match up with home-cooked foodsDr Charlotte Wright, Lead Researcher

Babies have an innate preference for sweet foods, which might explain why sweet ingredients feature so prominently in commercial products, said Dr Charlotte Wright and her team in Archives of Disease in Childhood.

The aim of weaning is to introduce babies to a wider range of tastes, textures, and flavours, to encourage them to accept different foods, and to boost their energy and nutrient intake as they make the transition from breast milk.

Sweet tooth

UK experts say weaning should not be started before six months, in line with recommendations for exclusive breastfeeding until that time.

Dr Wright and her team found that many weaning products sold in the UK are promoted for infants from the age of four months.

And the majority are no more energy-dense than breast or formula milk.

We recognise that some parents choose to wean their baby before six months of age, which is why some baby foods provide information that those foods can be given 'from four months' on their labelsThe British Specialist Nutrition Association

Commercial rusks and biscuits were much more energy-dense and contained high amounts of iron and calcium, but also tended to be high in sugar, the researchers found.

The savoury "spoonable" commercial foods generally had much lower nutrient density than home-blended dinners, with the exception of iron content.

Babies would need to eat twice as much shop-bought food to get the same energy and protein as meals cooked at home, according to the research.

Dr Wright said that while it was understandable that parents may choose to use commercial foods they should be aware of what is in them.

"People might think that something sweetened with fruit is healthier, but it's not. Young babies like sweet food because it tastes like breast milk but it is not moving them on.

"It's processed food that's been put in a jar so it's not that surprising that it does not match up with home-cooked foods."

Conflicting messages

The British Specialist Nutrition Association, which represents baby food manufacturers in the UK, said: "Baby foods are carefully prepared to ensure they provide the right balance of nutrients in appropriate amounts for infants and young children.

"Levels of protein, carbohydrate (including sugars), fat, vitamins and minerals in baby foods are strictly regulated by legislation which is based on advice from European scientific experts.

"Our member companies comply with the legislation as an absolute minimum.

"We recommend that commercial baby foods are used as part of a mixed diet which includes homemade foods plus breast milk or formula, which remain the most important source of nutrition for infants under 12 months."

A spokeswoman said that in Europe, experts advise that a baby is ready to be weaned at around four to six months.

"We recognise that some parents choose to wean their baby before six months of age, which is why some baby foods provide information that those foods can be given 'from four months' on their labels.

"We recommend that parents seek advice from a healthcare professional when thinking of starting weaning," she said.

Elizabeth Duff, of the National Childbirth Trust, said: "Many parents find that jars of baby food can be quick and convenient when you are out and about, but this new research shows that parents are potentially being misled about the health benefits.

"It is time baby food manufacturers stopped confusing parents by labelling their products as suitable from four months."

Heinz said generations of parents had trusted its food, while Cow & Gate said their foods complied with strict legal standards. Boots said their range offered a safe and nutritionally appropriate choice, and Organix said its foods were "complementary" to breastfeeding. Ella's Kitchen said its products were aimed to encourage young children to have a better relationship with food so that they grow up with healthy eating habits.